Remove class specifier prefixing Location in function declarations

[srmainwaring]

Remove occurrences of class prefixing Location in function declarations:

• See comment in: Plane: handle guided path requests in GUIDED mode #26328 (comment)

[rmackay9]

I'm happy with this but 3 of the 4 commits are outside my area so I've marked for next week's dev call. I suspect @peterbarker knows best if there's any difference in having the "class" in the front or not.

[nexton-winjeel]

if there's any difference in having the "class" in the front or not.

AFAIK having the class there makes it a forward declaration.

[peterbarker]

These header files are not including AP_Common/Location.h

That means they know this thing is a class only because they're getting that information transitively, and that's bad.

We do not want to include Location.h if we don't need to as it just slows things down unnecessarily.

I don't think this PR is a good idea.

Stripping them out where not required in e.g. .cpp files is a good idea, but not in headers if we then need to get the class aspect from elsewhere

[rmackay9]

OK, thanks very much for the education on this issue! Sorry @srmainwaring for the extra work but we all learned something perhaps :-)

[srmainwaring]

Stripping them out where not required in e.g. .cpp files is a good idea, but not in headers if we then need to get the class aspect from elsewhere

How about we forward declare class Location at the top of the file after the include directives rather than inline in function declarations? That makes the intent clearer. This started out as a request to clean up a function declaration in a different PR, so there is some confusion.

We do not want to include Location.h if we don't need to as it just slows things down unnecessarily.

The code base does not seem to generally apply forward declaration rules for compilation efficiency (as per J. Lakos, Large-scale C++ Software Design). Is that something we'd want to move to (or is that largely outdated now with the current round of compilers)?